Two small lymphocyte subpopulations in human peripheral blood. II. Functional characterization in vitro

Two small lymphocyte subpopulations from human peripheral blood were produced by rosette sedimentation procedures, and tested for in vitro functions by stimulation with mitogens, PPD and allogeneic lymphocytes, and for effector capacities in ADCC. The non-T, non-Fc subpopulation had previously been found to be a SmIg+ fraction which did not aquire new surface markers during unstimulated culture, did not respond to mitogens, PPD or allogeneic cells but were potent MLC stimulators. In addition, they were poor ADCC effector cells. The non-T, non-B ('Null') cells, which showed varying surface marker profiles from donor to donor, were able to respond to mitogens and PPD, but were weak MLC responders. Potent ADCC effector capacity was, however, found to be exhibited by this subpopulation.